1. Technical Field
The present invention relates to a vertical machine tool such as a vertical machining center, a vertical milling machine, etc. in which a main spindle thereof is provided vertically to a main spindle head, and more specifically to a vertical machine tool which can improve the set-up (preparatory) workability.
2. Description of the Related Art
In conventional machine tools such as vertical machining centers, vertical milling machines, etc., a main spindle is rotatably supported by a main spindle head, and the main spindle head is supported by a column so as to be movable in the vertical direction. Further, a worktable is arranged so as to be movable in a horizontal plane relative to the main spindle head. In the case of the vertical machining center of fixed column type, for instance, the main spindle head is supported by a fixed column so as to be movable in a Z-axis (vertical) direction, and the worktable is arranged so as to be movable relative to the main spindle head in both the horizontal X-axis (right and left) and Y-axis (front and rear) directions, when seen from the front of the machine tool.
In the above-mentioned vertical machining center, work on the worktable can be located in position by moving the worktable in both the X- and Y-axis directions, and after that the work on the worktable can be processed by use of a tool attached to the main spindle rotatably supported by the main spindle head.
In the conventional vertical machine tool as described above, the stroke end position of the worktable in both X- and Y-axis directions are determined in such a way that the innermost edge portions of the worktable are located at a position under the main spindle. This is because the work can be processed, even if the worktable is moved at the maximum strokes thereof. Further, this is because it possible to minimize the size of the bed for supporting the worktable movable relative to the main spindle head.
In the conventional vertical machine tool, when work is mounted on the worktable by use of a pendent material handling machine (e.g., crane, hoist, etc.) for set-up (preparatory) work, the worktable is moved to the stroke end position in the Y-axis direction and after that a hook of the material handling machine is lowered. In this case, in the conventional vertical machine tool, since the innermost edge portion of the worktable is determined at the central position of the main spindle, there exists a problem in that the hook of the material handling machine interferes with the main spindle head. Accordingly, at the set-up work, the worker must take care of the collision of the hook with the main spindle head, thus deteriorating the work set-up workability.
Further, in the worktable of the machine tool, a plurality of T-shaped grooves for mounting jigs (T-bolts) or vises are usually formed in the upper surface of the worktable so that work can be fixed to the worktable with the jigs or vises. In the conventional worktable, in general, the T-shaped grooves are mainly formed so as to extend in the X-axis (right and left) direction of the machine tool when seen from the front side thereof. For example, when the worktable is 1600 mm in the X-axis direction and 700 mm in the Y-axis (front and rear) direction, six T-shaped grooves with a width of 18 mm are formed so as to extend in the X-axis direction in parallel to each other, and a single T-shaped groove with the same width is formed so as to extend in the Y-axis direction at roughly the middle position of the worktable.
In the conventional worktable, however, since the six T-shaped grooves extending in the X-axis direction are longer than the single T-shaped groove extending in the Y-axis direction, there exists a problem in that the worker must move over a relatively long distance along the long T-shaped grooves extending in the X-axis direction, whenever jigs or vises are required to be mounted on the worktable, with the result that it takes a long time to mount jigs or vises and clean the T-shaped grooves. In addition, since the Y-axis length of the worktable is usually shorter than the X-axis length thereof, the number of the T-shaped grooves extending in the X-axis direction is inevitably limited to a small numbers so that the vise mounting positions are relatively limited.